Download CH 56 powerpoint

Biogeography
56
Biogeography
• Introduction
• Earth’s Biogeographic Regions
• History and Biogeography
• Ecology and Biogeography
• Terrestrial Biomes
• Aquatic Biogeography
• Regional Patterns of Species Richness
• Biogeography and Human History
56
Introduction
• Darwin predicted that species that are widespread
would be more abundant and variable than
species with narrow distributions.
• Widespread species are often more abundant
locally, but no species is found everywhere.
• Biogeography is the study of the patterns of
distribution of populations, species, and
communities across Earth.
56
Earth’s Biogeographic Regions
• The question of why a species occurs in a
particular location has two possible answers:
 It evolved there or it moved there from
elsewhere.
 If a species is absent, either it was never there
or it was once present but no longer lives
there.
• Biogeographers interpret a wide array of
information to explain the distribution of the
organisms.
• This includes information about evolutionary
history, continental drift, glacial advances/retreats,
sea level changes, and mountain building.
56
Earth’s Biogeographic Regions
• Earth can be divided into several major
biogeographic regions.
• A species found only in a certain region is
endemic to that region.
• Remote islands such as Madagascar typically
have distinctive endemic biotas because water
barriers greatly restrict migration.
• Most species are confined to a single
biogeographic region, but Homo sapiens is the
most widespread species on Earth today.
Figure 56.1 Major Biogeographic Regions
56
History and Biogeography
• Past events influence the distribution of species
on Earth.
• Early biogeographers, such as Linnaeus, believed
that the continents were fixed in their positions,
and that all organisms were created in one place
from which they later dispersed.
56
History and Biogeography
• In 1912, Alfred Wegener proposed the idea of
continental drift, based on several observations:
 The shapes of the continents (e.g., Africa and
South America) seem to fit together like a
puzzle.
 The alignment of mountain chains, rock strata,
and glacial deposits suggest movement over
time.
 The distribution of organisms on Earth is hard
to explain if one assumes the continents never
moved.
56
History and Biogeography
• About 280 million years ago in the Permian
period, the continents were united in a land mass
called Pangaea.
• By 100 million years ago during the Cretaceous
period, Pangaea had separated into northern
(Laurasia) and southern (Gondwana) land
masses.
• Throughout the history of life, continental drift has
separated and combined biotas, greatly
influencing the distribution of species.
Figure 22.15 Positions of the Continents during the Cretaceous Period
56
History and Biogeography
• Area phylogenies are used to describe when
and where evolutionary lineages originated.
• To generate an area phylogeny, the names in a
taxonomic phylogeny are replaced with the names
of the places where those taxa live or lived.
• An area phylogeny suggests that horses
speciated as they moved from Africa to Asia.
• To infer the approximate times of separation of
lineages, biogeographers use molecular
difference between species, fossils to determine
how long a taxon has been in an area, and the
distribution of living species.
Figure 56.3 Taxonomic Phylogeny to Area Phylogeny (Part 1)
Figure 56.3 Taxonomic Phylogeny to Area Phylogeny (Part 2)
Figure 56.3 Taxonomic Phylogeny to Area Phylogeny (Part 3)
56
History and Biogeography
• A vicariant event is the appearance of a barrier
that splits the range of a species.
• Vicariant events include sea level changes,
mountain building, and continental movement.
• If members of a species cross an existing barrier
and establish a new population, the species’
disjunct range is the result of dispersal.
56
History and Biogeography
• By studying a single evolutionary lineage as well
as distribution patterns among lineages, scientists
can discover the relative roles of vicariant events
and dispersal in determining today’s distribution
patterns.
• The longer an area has been isolated from other
areas, the more endemic taxa it is likely to have.
• Australia has been separated from other
continents for 65 million years and has the most
distinct biota on Earth.
• North America and Eurasia were joined together
for much of Earth’s history and have very similar
biotas.
56
History and Biogeography
• When several hypotheses can explain a pattern,
the parsimonious hypothesis (that which requires
the least number of unobserved events to explain it)
is generally preferred.
56
History and Biogeography
• An example is found in the distribution of the New
Zealand flightless weevil.
• The weevil and other flightless insects are found
on the north and south islands of New Zealand.
• Geological evidence suggests that the tip of the
north island was once connected to the south
island.
• Therefore, it is more likely that a vicariant event
(separation of the land) allowed the dispersal of
the weevil and the other animals than that
individual crossings of Cook Strait did.
Figure 56.4 A Vicariant Distribution Explained
56
Ecology and Biogeography
• The climate of a region is the average of the
atmospheric conditions found there over time.
• Climates vary greatly on Earth and influence the
geographic distribution of species.
56
Ecology and Biogeography
• Solar energy inputs drive global climates.
• Every place on Earth receives the same total
number of hours of sunlight each year, but not the
same amount of energy.
• The rate at which solar energy arrives at the
Earth’s surface depends primarily on the angle of
the sunlight. At high latitudes, solar energy inputs
vary greatly throughout the year.
• Mean air temperature decreases about 0.4C for
every degree of latitude.
• Air temperature also decreases with elevation.
56
Ecology and Biogeography
• Earth’s climates are strongly influenced by global
air circulation patterns which result from global
variation in solar input.
• Air rises when heated and releases moisture.
Warm air rises in the Tropics and is replaced by
air flowing towards the equator from north and
south. The intertropical convergence zone is
where these air masses come together.
• Heavy rains usually fall in a region when it is close
to the intertropical convergence zone.
• This zone shifts latitudinally with the seasons,
resulting in patterns of rainy and dry seasons.
Figure 56.5 Rainy and Dry Seasons Change with Latitude
56
Ecology and Biogeography
• Air masses descend at 30 north and south. This
air is cool and has lost its moisture. Many deserts
are located at these latitudes.
• The movements of air masses are responsible for
global wind patterns.
• The spinning of Earth on its axis also influences
surface winds. Air masses are deflected to the
right in the Northern Hemisphere and to the left in
the Southern Hemisphere.
Figure 56.6 The Circulation of Earth’s Atmosphere
56
Ecology and Biogeography
• When air encounters mountain ranges, it rises,
cools, and drops moisture on the windward slopes
resulting in a precipitation distribution called a
rain shadow where the leeward slopes are dry.
Figure 56.7 A Rain Shadow
56
Ecology and Biogeography
• Global wind circulation patterns drives the
circulation of ocean water.
• Ocean water generally moves in the direction of
the prevailing winds.
• Winds blowing toward the equator cause warm
water to converge at the equator and move west
until it encounters a landmass.
• When warm equatorial water encounters a
landmass, it splits and moves north or south; this
is a major mechanism of heat transfer to high
latitudes.
Figure 56.8 Global Oceanic Circulation
56
Terrestrial Biomes
• Ecologists classify communities of organisms into
biomes.
• Biomes are major ecosystem types based on the
structure of the dominant vegetation.
• The vegetation of a biome has a similar
appearance wherever that biome is found on
Earth.
• The distribution of biomes on Earth is influenced
by annual patterns of temperature and rainfall.
• Each biome has a characteristic climate,
seasonality, and vegetation, and typical patterns
of species richness.
Figure 56.9 Biomes Have Distinct Geographic Distributions
56
Terrestrial Biomes
• The tundra biome is found in the Arctic and high
on mountains.
• In the Arctic, permanently frozen soil
(permafrost) underlies tundra vegetation.
• Plants grow only during the short summers when
the first few centimeters of permafrost melt.
• Lowland Arctic tundra is very wet because water
cannot drain through the permafrost.
• Arctic tundra animals either migrate into the area
for the summer only or are dormant for most of
the year.
Biomes: Tundra (Part 1)
Biomes: Tundra (Part 2)
56
Terrestrial Biomes
• Tropical alpine tundra is not underlain by
permafrost, so photosynthesis and other
biological activities continue throughout the year
and more plant forms are present.
56
Terrestrial Biomes
• The boreal forest biome is found south of the
tundra biome and at lower elevations on temperatezone mountains.
• Winters are long and very cold, while summers are
short and warm.
• The short summer favors trees with evergreen
leaves.
• Boreal forests have only a few tree species.
• Northern Hemisphere forests are dominated by
coniferous evergreen gymnosperms.
• Southern Hemisphere forests are dominated by
beech trees.
Biomes: Boreal Forest (Part 1)
Biomes: Boreal Forest (Part 2)
56
Terrestrial Biomes
• The temperate deciduous forest biome is found
in eastern North America, eastern Asia, and
western Europe.
• Temperatures fluctuate dramatically from season
to season.
• Precipitation is evenly distributed throughout the
year.
• Deciduous trees lose their leaves during the
winter.
• Many more tree species are present relative to
boreal forests.
Biomes: Temperate Deciduous Forest (Part 1)
Biomes: Temperate Deciduous Forest (Part 2)
56
Terrestrial Biomes
• The temperate grassland biome is found in
many parts of the world, all of which are relatively
dry much of the year.
• Most grasslands have hot summers and cold
winters.
• Grasslands are structurally simple, but they are
rich in species of perennial grasses, sedges, and
forbs. Grassland plants are adapted to grazing
and fire.
• Most of the grassland biome has been converted
to agriculture.
Biomes: Temperate Grasslands (Part 1)
Biomes: Temperate Grasslands (Part 2)
56
Terrestrial Biomes
• The cold desert biome is found in dry regions at
middle to high latitudes.
• Cold deserts are also found at high altitudes in the
rain shadows of mountain ranges.
• Seasonal temperatures vary greatly.
• Cold deserts are dominated by a few species of
low-growing shrubs.
• The most common taxa in the biome are seedproducing plants, birds, ants, and rodents.
Biomes: Cold Desert (Part 1)
Biomes: Cold Desert (Part 2)
56
Terrestrial Biomes
• The hot desert biome is found in two belts,
centered around 30 north and 30 south
latitudes.
• Central Australia and the middle of the Sahara
Desert are the driest regions within the biome.
• Except in the driest regions, hot deserts have
richer and more diverse vegetation than cold
deserts do.
• Succulent plants that store large quantities of
water in their stems are common. Annual plants
germinate and grow when rain falls.
Biomes: Hot Desert (Part 1)
Biomes: Hot Desert (Part 2)
56
Terrestrial Biomes
• The chaparral biome is found on the west sides
of continents at moderate latitudes, where cool
ocean waters flow offshore.
• The Mediterranean region of Europe, coastal
California, and central Chile are examples of
chaparral.
• Low-growing shrubs and trees with evergreen
leaves are the most common plants in chaparral.
The vegetation is adapted to periodic fires.
• Large populations of small seed-eating rodents
are present in the biome.
Biomes: Chaparral (Part 1)
Biomes: Chaparral (Part 2)
56
Terrestrial Biomes
• Thorn forests are found on the equatorial sides
of hot deserts. The climate is semi-arid with little
or no rain in winter, but sometimes heavy rain in
summer.
• The dominant plants are spiny shrubs and small
trees. Acacia is common.
• Savannas are found in dry tropical and
subtropical regions of Africa, South America, and
Australia.
• The savanna biome is characterized by its vast
expanses of grassland and scattered trees, and
by huge numbers of grazing and browsing
mammals.
Biomes: Thorn Forest and Tropical Savanna (Part 1)
Biomes: Thorn Forest and Tropical Savanna (Part 2)
56
Terrestrial Biomes
• The tropical deciduous forest biome is found
closer to the equator relative to thorn forests and
has a long summer rainy season.
• Species richness is moderate for plants and high
across all other categories, including mammals,
birds, reptiles, and amphibians.
• The tropical deciduous forest biome has some of
the best soils in the tropics for agriculture. Most of
it has been cleared.
Biomes: Tropical Deciduous Forest (Part 1)
Biomes: Tropical Deciduous Forest (Part 2)
56
Terrestrial Biomes
• Tropical evergreen forests are found in
equatorial regions where total rainfall exceeds
250 cm annually.
• The biome is the richest on Earth in both plant
and animal species.
• Overall productivity of tropical evergreen forests is
the highest among terrestrial ecological
communities.
• There are many epiphytes, plants that grow on
other plants and derive nutrients and moisture
from air and water.
Biomes: Tropical Evergreen Forest (Part 1)
Biomes: Tropical Evergreen Forest (Part 2)
56
Aquatic Biogeography
• Three-fourths of Earth’s surface is covered by
water.
• The oceans represent one large interconnected
water mass with no obvious barriers for dispersal.
• Fresh water is divided into river basins and
thousands of relatively isolated lakes.
• Terrestrial habitats are a barrier to dispersal of
freshwater aquatic organisms.
56
Aquatic Biogeography
• About 2.5 percent of Earth’s water is found in
ponds, lakes, and streams.
• Freshwater ecosystems contain about 10 percent
of all aquatic species.
• More than 25,000 insect species such as
dragonflies have at least one aquatic stage in
their lives (usually the larva).
• Most families of freshwater fishes are restricted to
a single continent due to the saltwater barrier
presented by Earth’s oceans.
56
Aquatic Biogeography
• Ocean water moves in great circular patterns
which determine biogeographic patterns.
• Most marine organisms have restricted ranges.
• Water temperature and salinity can be barriers to
dispersal of marine organisms.
• Deep ocean waters prevent the dispersal of
marine organisms that live only in shallow water.
• Richness of shallow-water species near isolated
islands of the Pacific decreases with distance
from the larger islands of Indonesia.
Figure 56.10 Oceanic Biogeographic Regions are Determined by Ocean Currents
Figure 56.11 Generic Richness of Reef-Building Corals Declines with Distance from Indonesia
56
Regional Patterns of Species Richness
• Species richness increases with area sampled.
• If the sampling area crosses a biogeographic
boundary, the rate at which new species are
counted increases.
Figure 56.12 Species Richness Increases with Area Sampled
56
Regional Patterns of Species Richness
• One of the first geographic patterns of species
richness observed was that more species are
present in low latitudes than high latitudes.
• More species are found in mountainous regions
than in relatively flat areas because more
vegetation types and climates exist in the
mountains.
Figure 56.13 The Latitudinal Gradient of Species Richness of North American Mammals
56
Regional Patterns of Species Richness
• Species richness on islands is always less than
an equivalent area of the mainland.
• Species richness on islands is positively
correlated with island size and inversely
correlated with distance from the mainland.
Figure 56.14 Small, Distant Islands Have Fewer Bird Species
56
Regional Patterns of Species Richness
• Over periods of a few hundred years, species
richness is influenced by immigration of new
species and the extinction of existing species.
• The MacArthur-Wilson model relates species
richness to immigration and extinction on an
island.
• The rate of arrival of new species and the rate of
extinctions of species already present determine
the equilibrium number of species on an island.
• The rate of immigration and extinction on an
island is affected by the size of the island and
distance from the mainland.
Figure 56.15 MacArthur and Wilson’s Model of Species Richness on Islands (Part 1)
56
Regional Patterns of Species Richness
• MacArthur and Wilson’s model can be used to
predict how species richness will vary among
islands of different sizes and distance from the
mainland.
• The number of species should be highest for
islands that are relatively large and closest to the
mainland.
Figure 56.15 MacArthur and Wilson’s Model of Species Richness on Islands (Part 2)
56
Regional Patterns of Species Richness
• Major disturbances can sometimes serve as
“natural experiments.”
• The eruption of Krakatau in 1883 destroyed all life
on the island’s surface, but it provided a test of
the MacArthur and Wilson model.
• By 1933 the island was again covered by a
tropical evergreen forest.
• While forest canopy was recovering, there were
high rates of colonization. Today, rates of
colonization are not as fast, but colonization and
extinctions are still occurring.
Table 56.1 Number of Species of Resident Land Birds of Krakatau
56
Biogeography and Human History
• The distributions of land masses and species on
Earth have had a strong influence on human
history.
• In recent times, human populations from Eurasia
have come to dominate other cultures.
Biogeography contributed to this.
• Eurasia happened to have a large number of
plants (large-seeded grasses) and animals
suitable for domestication.
• Thirteen large mammal species, including pigs,
horses, cattle, sheep, goats, and camels, were
domesticated in Eurasia.
56
Biogeography and Human History
• No animals were domesticated in Africa, and only
the llama was domesticated in the Americas.
• For domestication, large mammals needed three
characteristics: herding lifestyles, male-dominated
hierarchies, and a lack of territoriality. The large
mammals of Africa all lacked at least one of these
traits.
• Domesticated animals provided food and labor for
farming.
56
Biogeography and Human History
• Domestication of large mammals also introduced
diseases such as smallpox and measles to the
human population.
• Eurasian people acquired immunity to these
diseases.
• When Europeans colonized the New World, they
exposed the indigenous people to smallpox and
measles, and without immunity, many indigenous
people died.
56
Biogeography and Human History
• In Eurasia, most mountain ranges are oriented
east–west; therefore, dispersal of people was
relatively easy.
• Humans dispersed only recently into North
America across the Bering Land Bridge. The only
domesticated animal they brought was the dog.
• There were few species of grasses with large
seeds in North America. Maize came to
dominate, but it was difficult to domesticate.